Neurosurgery residency and fellowship education in the United States: 2 decades of system development by the One Neurosurgery Summit organizations.

The purpose of this report is to chronicle a 2-decade period of educational innovation and improvement, as well as governance reform, across the specialty of neurological surgery. Neurological surgery educational and professional governance systems have evolved substantially over the past 2 decades with the goal of improving training outcomes, patient safety, and the quality of US neurosurgical care. Innovations during this period have included the following: creating a consensus national curriculum; standardizing the length and structure of neurosurgical training; introducing educational outcomes milestones and required case minimums; establishing national skills, safety, and professionalism courses; systematically accrediting subspecialty fellowships; expanding professional development for educators; promoting training in research; and coordinating policy and strategy through the cooperation of national stakeholder organizations. A series of education summits held between 2007 and 2009 restructured some aspects of neurosurgical residency training. Since 2010, ongoing meetings of the One Neurosurgery Summit have provided strategic coordination for specialty definition, neurosurgical education, public policy, and governance. The Summit now includes leadership representatives from the Society of Neurological Surgeons, the American Association of Neurological Surgeons, the Congress of Neurological Surgeons, the American Board of Neurological Surgery, the Review Committee for Neurological Surgery of the Accreditation Council for Graduate Medical Education, the American Academy of Neurological Surgery, and the AANS/CNS Joint Washington Committee. Together, these organizations have increased the effectiveness and efficiency of the specialty of neurosurgery in advancing educational best practices, aligning policymaking, and coordinating strategic planning in order to meet the highest standards of professionalism and promote public health.

Surgical neurology: Harvey Cushing's endangered legacy.

As it does periodically, the United States healthcare system is, yet again, undergoing a period of change on multiple fronts, including internal initiatives in education, quality, and the workforce, as well as external pressure responding to changes in reimbursement and oversight. In such times, looking back at the foundations of our specialty is helpful, allowing often-beleaguered neurosurgeons to reflect upon what it means to be a neurosurgeon, and how they can be assured that our specialty will continue to flourish in the future. Harvey Cushing envisioned, espoused, and developed neurological surgery as a "special field"-a comprehensive, encompassing, and distinct discipline that studies the nervous system and manages neurological disorders. It provides surgical intervention for the treatment of neurological disorders; it by no means was meant to be developed as a mere technical or procedural skill; it is neither a subspecialty of surgery nor a branch of neurology; it is a "special field" that has flourished to become a crown jewel in the realm of medicine. Herein is a perspective that brings the inception and future of this concept to light. A specialty that is to live and flourish should stand on and recognize its roots.

Smart stylet: the development and use of a bedside external ventricular drain image-guidance system.

BACKGROUND: Placement accuracy of ventriculostomy catheters is reported in a wide and variable range. Development of an efficient image-guidance system may improve physician performance and patient safety. OBJECTIVE: We evaluate the prototype of Smart Stylet, a new electromagnetic image-guidance system for use during bedside ventriculostomy. METHODS: Accuracy of the Smart Stylet system was assessed. System operators were evaluated for their ability to successfully target the ipsilateral frontal horn in a phantom model. RESULTS: Target registration error across 15 intracranial targets ranged from 1.3 to 4.6 mm (mean 3.1 mm). Using Smart Stylet guidance, a test operator successfully passed a ventriculostomy catheter to a shifted ipsilateral frontal horn 20/20 (100%) times from the frontal approach in a skull phantom. Without Smart Stylet guidance, the operator was successful 4/10 (40%) times from the right frontal approach and 6/10 (60%) times from the left frontal approach. In a separate experiment, resident operators were successful 2/4 (50%) times when targeting the shifted ipsilateral frontal horn with Smart Stylet guidance and 0/4 (0%) times without image guidance using a skull phantom. CONCLUSIONS: Smart Stylet may improve the ability to successfully target the ventricles during frontal ventriculostomy.

Resident away rotations allow adaptive neurosurgical training.

Subspecialization of physicians and regional centers concentrate the volume of certain rare cases into fewer hospitals. Consequently, the primary institution of a neurological surgery training program may not have sufficient case volume to meet the current Residency Review Committee case minimum requirements in some areas. To ensure the competency of graduating residents through a comprehensive neurosurgical education, programs may need for residents to travel to outside institutions for exposure to cases that are either less common or more regionally focused. We sought to evaluate off-site rotations to better understand the changing demographics and needs of resident education. This would also allow prospective monitoring of modifications to the neurosurgery training landscape. We completed a survey of neurosurgery program directors and query of data from the Accreditation Council of Graduate Medical Education to characterize the current use of away rotations in neurosurgical education of residents. We found that 20% of programs have mandatory away rotations, most commonly for exposure to pediatric, functional, peripheral nerve, or trauma cases. Most of these rotations are done during postgraduate year 3 to 6, lasting 1 to 15 months. Twenty-six programs have 2 to 3 participating sites and 41 have 4 to 6 sites distinct from the host program. Programs frequently offset potential financial harm to residents rotating at a distant site by support of housing and transportation costs. As medical systems experience fluctuating treatment paradigms and demographics, over time, more residency programs may adapt to meet the Accreditation Council of Graduate Medical Education case minimum requirements through the implementation of away rotations.

Factors associated with external ventricular drain placement accuracy: data from an electronic health record repository.

BACKGROUND: We evaluated external ventricular drain placement for factors associated with placement accuracy. Data were acquired using an electronic health record data requisition tool. METHOD: Medical records of all patients who underwent ventriculostomy from 2003 to 2010 were identified and evaluated. Patient demographics, diagnosis, type of guidance and number of catheter passes were searched for and recorded. Post-procedural hemorrhage and/or infection were identified. A grading scale was used to classify accuracy of catheter placements. A multiple logistic regression model was developed to assess features associated with accurate catheter placement. RESULTS: One hundred nine patients who underwent 111 ventriculostomies from 2003 to 2010 were identified. Patient diagnoses were classified into vascular (63 %), tumor (21 %), trauma (14 %), and cyst (2 %). Procedures were performed freehand in 90 (81 %), with the Ghajar guide in 17 (15 %), and with image guidance in 4 (4 %) patients. Eighty-eight (79 %) catheters were placed in the correct location. Trauma patients were more likely to have catheters misplaced (p = 0.007) whereas patients in other diagnostic categories were not significantly associated with misplaced catheters. Post-procedural hemorrhage was noted in 2 (1.8 %) patients on post-procedural imaging studies. Five (4.5 %) definite and 6 (5.4 %) suspected infections were identified. CONCLUSIONS: External ventricular drain placement can be performed accurately in most patients. Patients with trauma are more likely to have catheters misplaced. Further development is required to identify and evaluate procedure outcomes using an electronic health record repository.

Philanthropy funding for neurosurgery research and program development.

In times of fiscal and political uncertainty, philanthropy has become an increasingly important mechanism for building, maintaining, and expanding neurosurgical research programs. Although philanthropy has historically helped launch many hospital systems, scientists and clinicians have generally relied on government grants and industry investment to support research and program infrastructure. However, competition for funds from all sources has increased at the same time as the pipelines for those funds have eroded. Philanthropy can provide salary support to allow neurosurgeons to pursue research and, ultimately, advance the field to improve outcomes for patients. Funds raised can fill financial gaps to recruit and pay for needed research staff, equipment, and facilities. To foster charitable giving, institutions can develop both a culture and processes to promote and support philanthropy. Furthermore, it is essential to ensure that donor relationships are properly nurtured with ongoing stewardship. In addition to cultivating grateful patients, there are numerous creative models of fundraising for research that can be explored, including venture philanthropy, in which voluntary health organizations or individuals partner with academia and industry to invest in early-stage drug development and other innovations. Other approaches include formation of nonprofit foundations and partnerships with other entities to work jointly on shared development goals.

Cerebral capillary telangiectasias: a meta-analysis and review of the literature.

As a result of their presumed benign natural history, cerebral capillary telangiectasias (CCTs) are infrequently addressed in the neurosurgical literature. We performed a comprehensive review of CCTs via the PubMed database to synthesize overall epidemiological, radiographic, natural history, and treatment results. Across ten series with 203 patients, mean age was 47, and 45 % were male [95 % confidence interval (CI), 0.30-0.65]. Notably, 78 % of CCTs were in the pons (95 % CI, 0.58-1.0). Six percent of CCTs were symptomatic. Across five radiographic series, all lesions enhanced after gadolinium, and all were hypointense on gradient echo sequences. Thirty-three percent were hypointense on T1-weighted pre-contrast imaging (95 % CI, 0.2-0.51), 49 % were hyperintense on T2-weighted imaging (95 % CI, 0.31-0.72), and 74 % were hypointense on diffusion-weighted imaging (95 % CI, 0.5-1.0). Notably, 37 % were associated with a prominent draining vein (95 % CI, 0.21-0.6), and 11 % with a developmental venous anomaly (95 % CI, 0.04-0.25). Across four observational studies with 47 patients, there was no observed change in lesion morphology or hemorrhage in 65.7 patient-years of follow-up. Although the vast majority of CCTs are managed conservatively, we found ten cases of patients treated with surgical excision. We confirm that CCTs are a benevolent entity with a predilection for the pons. They have distinctive radiographic features including their lack of mass effect, consistent enhancement on T1-weighted sequences and hypointensity on gradient echo sequences, and common isointensity on pre-contrast T1-weighted and T2-weighted images. Management for these lesions has been nonoperative in almost all cases.

Patterns in neurosurgical adverse events and proposed strategies for reduction.

Neurosurgery is a high-risk specialty currently undertaking the pursuit of systematic approaches to reducing risk and to measuring and improving outcomes. The authors performed a review of patterns and frequencies of adverse events in neurosurgery as background for future efforts directed at the improvement of quality and safety in neurosurgery. They found 6 categories of contributory factors in neurosurgical adverse events, categorizing the events as influenced by issues in surgical technique, perioperative medical management, use of and adherence to protocols, preoperative optimization, technology, and communication. There was a wide distribution of reported occurrence rates for many of the adverse events, in part due to the absence of definitive literature in this area and to the lack of standardized reporting systems. On the basis of their analysis, the authors identified 5 priority recommendations for improving outcomes for neurosurgical patients at a population level: 1) development and implementation of a national registry for outcome data and monitoring; 2) full integration of the WHO Surgical Safety Checklist into the operating room workflow, which improves fundamental aspects of surgical care such as adherence to antibiotic protocols and communication within surgical teams; and 3-5) activity by neurosurgical societies to drive increased standardization for the safety of specialized equipment used by neurosurgeons (3), more widespread regionalization and/or subspecialization (4), and establishment of data-driven guidelines and protocols (5). The fraction of adverse events that might be avoided if proposed strategies to improve practice and decrease variability are fully adopted remains to be determined. The authors hope that this consolidation of what is currently known and practiced in neurosurgery, the application of relevant advances in other fields, and attention to proposed strategies will serve as a basis for informed and concerted efforts to improve outcomes and patient safety in neurosurgery.

Stereotactic radiosurgery for cerebral dural arteriovenous fistulas.

OBJECT: Given the feasibility of curative surgical and endovascular therapy for cerebral dural arteriovenous fistulas (DAVFs), there is a relative paucity of radiosurgical series for these lesions as compared with their arteriovenous malformation counterparts. METHODS: The authors reviewed records of 56 patients with 70 cerebral DAVFs treated at their institution over the past 6 years. Ten DAVFs (14%) in 9 patients were treated with stereotactic radiosurgery (SRS), with follow-up obtained for 8 patients with 9 DAVFs. They combined their results with those obtained from a comprehensive review of the literature, focusing on obliteration rates, post-SRS hemorrhage rates, and other complications. RESULTS: In the authors' group of 9 DAVFs, angiographic obliteration was seen in 8 cases (89%), and no post-SRS hemorrhage or complications were observed after a mean follow-up of 2.9 years. Combining the results in these cases with data obtained from their review of the literature, they found 558 DAVFs treated with SRS across 14 series. The overall obliteration rate was 71%; transient worsening occurred in 9.1% of patients, permanent worsening in 2.4% (including 1 death, 0.2% of cases), and post-SRS hemorrhage occurred in 1.6% of cases (4.8% of those with cortical venous drainage [CVD]). The obliteration rate for cavernous DAVFs was 84%, whereas the rates for transversesigmoid and for tentorial DAVFs were 58% and 59%, respectively (adjusted p values, p(cav,TS) = 1.98 × 10(-4), p(cav,tent) = 0.032). Obliteration rates were greater for DAVFs without CVD (80%, compared with 60% for those with CVD, p = 7.59 × 10(-4)). Both transient worsening and permanent worsening were less common in patients without CVD than in those with CVD (3.4% vs 7.3% for transient worsening and 0.9% vs 2.4% for permanent worsening). CONCLUSIONS: Stereotactic radiosurgery with or without adjunctive embolization is an effective therapy for DAVFs that are not amenable to surgical or endovascular monotherapy. It is best suited for lesions without CVD and for cavernous DAVFs.

A national fundamentals curriculum for neurosurgery PGY1 residents: the 2010 Society of Neurological Surgeons boot camp courses.

BACKGROUND: In July 2009, the Accreditation Council for Graduate Medical Education (ACGME) incorporated postgraduate year 1 (PGY1 intern) level training into all U.S. neurosurgery residency programs. OBJECTIVE: To provide a fundamentals curriculum for all incoming neurosurgery PGY1 residents in ACGME-accredited programs, including skills, knowledge, and attitudes that promote quality, patient safety, and professionalism. METHODS: The Society of Neurological Surgeons organized 6 regional "boot camp" courses for incoming neurosurgery PGY1 residents in July 2010 that consisted of 9 lectures on clinical and nonclinical competencies plus 10 procedural and 6 surgical skills stations. Resident and faculty participants were surveyed to assess knowledge and course effectiveness. RESULTS: A total of 186 of 197 U.S. neurosurgical PGY1 residents (94%) and 75 neurosurgical faculty from 36 of 99 programs (36%) participated in the inaugural boot camp courses. All residents and 83% of faculty participants completed course surveys. All resident and faculty respondents thought that the boot camp courses fulfilled their purpose and objectives and imparted skills and knowledge that would improve patient care. PGY1 residents' knowledge of information taught in the courses improved significantly in postcourse testing (P < .0001). Residents and faculty particularly valued simulated and other hands-on skills training. CONCLUSION: Regional organization facilitated an unprecedented degree of participation in a national fundamental skills program for entering neurosurgery residents. One hundred percent of resident and faculty respondents positively reviewed the courses. The boot camp courses may provide a model for enhanced learning, professionalism, and safety at the inception of training in other procedural specialties.

Central nervous system agents for ischemic stroke: neuroprotection mechanisms.

Stroke is the third leading cause of mortality and disability in the United States. Ischemic stroke constitutes 85% of all stroke cases. However, no effective treatment has been found to prevent damage to the brain in such cases except tissue plasminogen activator with narrow therapeutic window, and there is an unmet need to develop therapeutics for neuroprotection from ischemic stroke. Studies have shown that mechanisms including apoptosis, necrosis, inflammation, immune modulation, and oxidative stress and mediators such as excitatory amino acids, nitric oxide, inflammatory mediators, neurotransmitters, reactive oxygen species, and withdrawal of trophic factors may lead to the development of the ischemic cascade. Hence, it is essential to develop neuroprotective agents targeting either the mechanisms or the mediators leading to development of ischemic stroke. This review focuses on central nervous system agents targeting these biochemical pathways and mediators of ischemic stroke, mainly those that counteract apoptosis, inflammation, and oxidation, and well as glutamate inhibitors which have been shown to provide neuroprotection in experimental animals. All these agents have been shown to improve neurological outcome after ischemic insult in experimental animals in vivo, organotypic brain slice/acute slice ex vivo, and cell cultures in vitro and may therefore aid in preventing long-term morbidity and mortality associated with ischemic stroke.

Tamoxifen as an effective neuroprotectant in an endovascular canine model of stroke.

OBJECT: Tamoxifen has been shown to be a potent neuroprotectant against stroke in rodents. Because other neuroprotectant medications have failed in human trials, a study of tamoxifen in a large-animal model was necessary to further assess the drug's effectiveness. For this study, the authors developed an endovascular model of anterior circulation infarction in canines to mimic the human clinical condition. They assessed the following hypotheses: 1) that they will be able to consistently produce an internal carotid artery (ICA) terminus infarction and 2) that tamoxifen is an effective neuroprotectant against stroke in canines. METHODS: In 24 male beagles (weight 9-11 kg), bilateral femoral artery cutdowns were performed, and the vertebral artery and left ICA were each selectively catheterized. Under fluoroscopic guidance, a microcatheter was introduced via the vertebral artery, guiding the catheter into the basilar artery, posterior communicating artery, and ICA terminus. A 1-ml clot was injected in the terminus, occluding the middle cerebral artery (MCA) and anterior cerebral artery (ACA) origin. In the first 12 canines, the occlusions were confirmed by angiography. A Canine Stroke Score (CSS) was assigned (score range 0-18 [0 = intact on examination, 18 = comatose]). The animals were then killed and their brains stained with 2,3,5-triphenyltetrazolium chloride (TTC). The subsequent 12 canines underwent a blinded randomized study in which the authors compared the results of tamoxifen (5 mg/kg) infused intravenously 1 hour after clot injection with an equal volume of vehicle (dimethylsulfoxide). After 3 hours, the animals underwent MR imaging, were extubated, and clinical examinations were performed. The canines were killed at 8 hours after clot injection, and TTC staining was used. RESULTS: In the first group, infarct volume and CSSs were consistent with the extent of the occlusion of the angiographic vessels. An occlusion of the ACA, MCA, and posterior cerebral artery resulted in larger infarcts and higher stroke scores than occlusion of the ACA and MCA. In the second group, tamoxifen significantly reduced infarct size and improved clinical outcomes. In tamoxifen-treated animals, the mean infarct volume reduction was 40% (p < 0.05) and the mean CSS was significantly less than vehicle-treated animals (p < 0.001). There were significant correlations among MR imaging-determined volume, TTC-determined volume, and neurological clinical outcome (p < 0.05). CONCLUSIONS: Using this endovascular model of stroke, the authors were able to consistently produce an infarction in the canines that was similar in scope to a carotid terminus occlusion in humans. Also, angiography could predict subsequent clinical course and infarct size. Tamoxifen was effective at significantly improving the canine neurological deficits and reducing the size of the stroke. This study took the first step in demonstrating the effectiveness of a promising human neuroprotectant in a large animal.

Intramedullary spinal cord cavernous malformations.

Although originally the subject of rare case reports, intramedullary spinal cord cavernous malformations (CMs) have recently surfaced in an increasing number of case series and natural history reports in the literature. The authors reviewed 27 publications with 352 patients to consolidate modern epidemiological, natural history, and clinical and surgical data to facilitate decision making when managing these challenging vascular malformations. The mean age at presentation was 42 years without a sex predilection. Thirty-eight percent of the cases were cervical, 57% thoracic, 4% lumbar, and 1% unspecified location. Nine percent of the patients had a family history of CNS CMs. Twenty-seven percent of the patients had an associated cranial CM. On presentation 63% of the patients had motor deficits, 65% had sensory deficits, 27% had pain, and 11% had bowel or bladder dysfunction. Presentation was acute in 30%, recurrent in 16%, and progressive in 54% of cases. An overall annual hemorrhage rate was calculated as 2.5% for 92 patients followed up for a total of 2571 patient-years. Across 24 reviewed surgical series, a 91% complete resection rate was found. Transient morbidity was seen in 36% of cases. Sixty-one percent of patients improved, 27% were unchanged, and 12% were worse at the long-term follow-up. Using this information, the authors review surgical nuances in treating these lesions and propose a management algorithm.

Surgonomics of unruptured intracranial aneurysms.

BACKGROUND/AIMS: A comparison of reimbursement for endovascular coil embolization and surgical clipping of unruptured aneurysms has not been previously reported. The aim of this study is to assess the reimbursement to physicians and hospitals for each of these two unruptured aneurysm treatments with long-term follow-up. METHODS: Hospital and physician payents were determined for 14 patients treated with coil embolization or surgical clipping of a single unruptured aneurysm per patient from 2004 to 2005, retrospectively. For this analysis, each considered hospital and physician payment encompassed one clipping or coiling procedure plus all pre- and post-operative diagnostic angiograms performed through 2007 to evaluate the treated aneurysm. Reimbursements were analyzed in three categories: physician payments, hospital payments and total payments. RESULTS: Average physician payments were significantly lower for coil embolization ($3422) than surgical clipping ($5645). Average length of stay after coil embolization was 2.6 days (range: 1-7) and after surgical clipping was 4.7 days (range: 2-11). The length of hospital stay directly affected hospital and total payments only, but was not significantly altered by which procedure was performed. CONCLUSION: This study suggests that physician payment for an unruptured aneurysm coil embolization treatment was statistically lower than for a surgical clip treatment. Although physicians were compensated at a lower rate for performing a coil embolization, there was no significant difference in the hospital or total payments between coil or clip treatment modalities.

Retrospective analysis of parenteral magnesium sulfate administration in decreased incidence of clinical and neuroradiological cerebral vasospasm: a single center experience.

OBJECTIVE: Experimental work suggests a neuroprotective role for magnesium sulfate in aneurysmal subarachnoid hemorrhage. We retrospectively review the incidence of clinically relevant vasospasm in patients treated or not with continuous magnesium infusion after onset of subarachnoid hemorrhage. METHODS: All patient records in Albany Medical Center with the diagnosis of SAH between January 1999 and June 2004 were reviewed. Patients who presented to the emergency department within 72 hours of onset were entered in the study. Patients were defined as in clinical vasospasm if there was an acute neurological change in association with abnormal trancranial Doppler (TCD), CT angiogram (CTA) or digital subtraction angiography (DSA). RESULTS: A total of 85 patients were selected. Magnesium sulfate was infused in 43 patients. When compared with patients who did not receive MgSO(4), there was a statistically significant lower incidence of clinical and radiological vasospasm in those who had the continuous infusion of magnesium sulfate (p<0.01). There was no statistically significant difference between patients who were coiled or clipped. CONCLUSION: Continuous magnesium sulfate infusion for the management of clinically significant cerebral vasospasm is safe and reduces the incidence of clinically significant cerebral vasospasm. Large, multicenter, controlled studies should be performed in order to determine the true effectiveness of the treatment in a controlled setting.

Peri-operative medical management of cerebral vasospasm.

INTRODUCTION: The physiological mechanism of cerebral vasospasm after aneurysmal subarachnoid hemorrhage remains elusive and its treatment can be challenging. Traditionally, 'triple-H' therapy and the calcium channel blocker, nimodipine, are used to treat cerebral vasospasm. However, as the etiology of vasospasm is unraveled, investigative pharmaceutical agents that stop the development and attenuate the severity of cerebral vasospasm, are being investigated in clinical trials. METHODS: In this manuscript, we review the clinical presentation and characteristics of cerebral vasospasm after aneurysmal subarachnoid hemorrhage and the utility of hyperdynamic therapy and pharmacotherapies. RESULTS: Triple-H therapy improves cerebral perfusion and improves neurological outcome during clinically evident cerebral vasospasm. Nimodipine is the accepted standard medication used to reduce the incidence of cerebral vasospasm, but more importantly, has a neuroprotective effect during hypoxia. Other medications such as magnesium sulfate, HMG-CoA reductase inhibitors and enoxaparin, are also being trialed with some promising results. CONCLUSION: Endovascular administration of intra-arterial anti-spasmodic agents and balloon angioplasty are becoming more commonly utilized at institutions where endovascular therapy is available. However, triple-H therapy and nimodipine remain the accepted first-line of treatment for cerebral vasospasm after aneurysmal subarachnoid hemorrhage.

Persisting embryonal infundibular recess.

Persisting embryonal infundibular recess (PEIR) is a rare anomaly of the third ventricular floor that has an unclear pathogenesis. In all 7 previously described cases, PEIR was present in adult patients and was invariably associated with hydrocephalus and, in 4 reported cases, with an empty sella. These associated findings led to speculations about the role of increased intraventricular pressure in the development of PEIR. In the present case, PEIR was found in a 24-year-old man without the presence of hydrocephalus or empty sella. Disorders of pituitary function had been present since childhood. Magnetic resonance imaging revealed a cystic expansion in an enlarged sella turcica. A communication between the third ventricle and the sellar cyst was suspected but not apparent. During transcranial surgery, the connection was confirmed. Later, higher-quality MR imaging investigations clearly showed a communication between the third ventricle and the sellar cyst through a channel in the tubular pituitary stalk. This observation and knowledge about the embryology of this region suggests that PEIR may be a developmental anomaly caused by failure of obliteration of the distal part of primary embryonal diencephalic evagination. Thus, PEIR is an extension of the third ventricular cavity into the sella. Although PEIR is a rare anomaly, it is important to identify when planning a procedure on cystic lesions of the sella. Because attempts at removal using the transsphenoidal approach would lead to a communication between the third ventricle and the nasal cavity, a watertight reconstruction of the sellar floor is necessary.